Hydraulic apparatus



April 4, 1950 C. E. ADAMS ETAL HYDRAULIC APPARATUS Filed May 11, 1948 3 Sheets-Sheet l I'I'llllllll JNVENTORS' S M A D A E H C E C Ap 1950 -c. E. ADAMS EIAL 2,502,547

. HYDRAULIC APPARATUS Fi led May 11, 1948 v s Sheets-Sheet a mam? 55 a! WA INVENTORS CECIL E. ADAMS BY WILLIAM D. PETERS z/WMIKMW April 4, 1950 c. ADAMS ETAL HYDRAULIC APPARATUS 3 Sheets-Sheet 3 Filed May 11, 1948 w, a 2 J 4 65 4 14 L a 5 v w m I P w w a & a? w a a g j MMW a BM? m INVENTORS CECIL E. ADAMS s R E T E P D M m L H W BY 7%5W Patented Apr. 4, 1950 PATENT 3,502,547 v HYDRAULIC APPARATUS Cecil'E. Adamsand'mllianrDs-Beters, Columbus,

'-.-Ohio, :assignors ate -:The Den-ison Engineering, sGompany, Gol-umbus, Ohio, we. corporation -.of

:11 .Glai-ms. 1

accompanied: by a decrease. in :the rate or qmotion ofrthe piston.

.:Another object OfT -thBELiI'IVQHtiOII is toprovide a hydraulic system-5 for hydrauliczapparatus having: afluid motor. of thepiston; and; cylinder-type, the motcbrbeingiso constructed that it :will include 1a pluralityofpistonsurfaces of differingareas, ithe system 1 including control mechanism byrmeans :of which. fluid displaced ".by certain -oi thev piston surfacesHwil-l be: combined withfluid applied'fuo-other piston surfaces to'decreaserthe efiectiueareas :of :thepiston :thus increasing rateiofzmovementithereof.

;Another;.objectrof:the invention is torprovidewa mechanismiofzthe character specifiedinthemreceding vparagraph and to, so iconstruct' a .icontrol mechanismthereforrthat the-combination of? fluid.

displacedxbetweenicertain piston surfaces-may be interrupted, 'xthe displaced fluid then beingcdirected to exhaust whereby the effective area 1' of the piston surface .to which "fluid :is being applied will :be increased .and "thus :increase -the force-exertedby thepiston.

Aistill furtherzobgect oi the inventionis to provide a .fluid :motor having .a casing formed with-a .cylinderforithe"reception of -a pistonand ram, the piston. and ram also beingrjformed: with a second cylinder for the reception oiea:.-seccnd piston which is rigidly carriedby the casing,;fluid conducting :and control mechanism being provided so that :fluid under pressure.=may.be.-applied to the first piston to:eiiect'movement-thera of, "the. fluid displaced by such piston :during movement being: combined with :fluidapplied dao efiect its movement whereby the piston will "be causedto move ata rapid rate, .thensecondipiston operating :in the second cylinder wserving as-.a pump, during".movementmfthe, first-piston; ini-one direction ito adraw rfluid from ea-.-su ita.b1e source amlizomthereturn movementiof the-:first..piston':to combine :this (flu-id iWlthf fluid from the pressure source applied to the first'pistonatoincrease the rate not .return :movement :of the piston; 'bylthe telescopic arrangement.ofithe pistons .ca high de-'. gree of vcompactness :in the 1' fluid :motor twill-thev secured.

.hnetherzobject of .the invention is z-to provide a hydrauliesystem'having azsource of ffluidrpres sure,..a fluidrmotor-ofgthe type..mentioned intthe preceding paragraph, a :control avalve; mechanism between thev fluid motor andizthezpressurewsource andtconduitsconnecting the rpressu-re source with. the control yalve mechanismanot the; lattenmechlanismrrwith certain portions 1.0! the "fluid :motor; conduits also being 1 provided :to connect certain portions hi .the cylinders of :.the fluid i-motor combinegfluid exhaust'edby theepistonswwithifluid applied .gby -the ,:pressure, source to decrease rthe e-mective areas 10f the :pistons and pauserapid movement thereof ;.val-v.ed' con-duitsalsogbeingmnovided so that! the; hy:draulic.;system may :berconuerted:intoiaeconventionalrsystem at will.

Further objects and advantages:ofzthe-tpresent invention will be apparent rfrom gthe' :following description, "reference being .aha-d to the accompanying idrawings wherein a preferred form cot embodiment Qf -the. inventioniis clearlyashown.

. .Inthe drawings: I

:E'ig'. .lisza diagrammaticiv-iewof: a-hydraulicsystemifermed in accordance with .the presentinvention; 1a fluid motor and control .:mechanism; therefor included in said: system being; shown in;

vertical section.

:Figs. 2, 3 and :4 arevertical: sectional views-0f the rcontrol 'v'alve :mechanism showing -the mov able elements" thereof in. different :operative po sitions. y I

Fig. 5' is a diagrammatic :v-iewof a .'modifiedl hydraulic-system, also including the featuresof the: present invention, sby which the operation. of the: hydraulicdeviee may. be modified.

Referring :more particularly to the drawingsthe hydraulic system shown in Fig, 1 is designatedgenerally; by the. numeraLZO. generalv the hydraul-ic. system .20 includes :a gpressureflsource 21., a hand :motor .12 2 and control mechanismior motor indicatedgenerally .by the numeral 23. The fluid. source has been indicated only fdi-- agrammatically and .includes .a reservoir 24,;21

tends from the outlet of the relief valve back to the reservoir 24 to return fluid thereto when the relief valve spills due to the pressure in line 28 approaching a predetermined maximum. A fluid line 3| extends from the relief valve to the inlet port 32 of the control valve mechanism 23, the port 32 being formed in the body 33 f the valve mechanism.

This body 33 includes a vertical chamber 34 and a plurality of annular grooves 35 to 39, in-' elusive, spaced longitudinally of the body and.

communicating with the chamber 34, groove 35 also communicating with the. port 32 and hereinafter being termed the inlet; or, pressure port. Grooves 36 and 31 are disposed at opposite sides of the groove 35 and are hereinafter designated as top and bottom cylinder ports. vWhile grooves 38 and 39 are disposed between the top and bottom cylinder ports and the ends of the body 33; grooves 38 and 39 are designated as exhaust ports. These grooves 38 and 39 are connected by a line 4| which in turn is connected by a branch line 32 with reservoir 24.

The top cylinder port 36 is connected by a line 43 with the upper end of a cylinder 44 which is formed in the casing 45 of the fluid motor 22, the bottom cylinder port 31 being connected by line 46 with the lower end of the cylinder 44. Cylinder 44 receives for sliding movement, a piston 41, which has a ram 48 depending therefrom, this ram extending through a cover 59 employed to close the open lower end of the cylinder 44. The diameter of the ram 48 is smaller than the diameter of the piston 41, thus providing a downwardly facing surface which is exposed to fluid supplied tothe lower end of the power cylinder. When pump 25 is operated fluid will be drawn from the reservoir 24 and discharged through lines 28 and 3| to the inlet port 35 of the control valve mechanism. The applicationof the fluid from the pump to the fluid motor or power cylinder is controlled by a spool member 52, which is disposed for movement in the chamber 34.

'.'The spool 52 in this instance is provided with four'longitudinally spaced grooves 53 to 56, inclusive. These grooves serve to connect certain of the grooves 35 to 39 in various positions ofadjustment of the spool 52. In the position shown in Fig. 1, spool 52 will direct the fluid supplied by the pressure source to the inlet port 32, to' exhaust and permit the fluid motor to remain idle with the piston 41 retracted in the cylinder 44. The fluid will flow in the direction of the arrows to Fig. 1 from .groove 35 to groove 36, through groove 56 to exhaust port 38, this fluid then flowing through lines 4| and 42 to the reservoir. When spool 52 is in position shown in Fig. 1, the groove 31 which is connected with the lower end of the power cylinder will be blocked off so that no fluid can be discharged therefrom the fluid then in the lower end of the cylinder 44 will retain the piston and ram in the elevated position.

Q'Io eifect movement of the spool 52, a shipper rod has been provided, this rod depending from the 'spool 52. Under normal conditions, the rod 51 an d spool52 are urged in a downward direction by "a coil spring 58 arranged between the lower end of the body 33 and a collar 59 secured to the shipper rod. When the piston 41 and ram are in an elevated position as shown in Fig. 1, the spool 52 will be held in a partially elevated position against the force of spring 58 by an arm 6|,"whichis secured to the ram 48 and sur- 4 rounds the shipper rod, this arm engaging a collar 62 adjustably carried by the rod 51.

In the form of the invention illustrated, an operating lever 63 is pivotally connected to the lower end of rod 51 and is pivoted for rocking movement as at 64, the lever 63 being provided with an operating knob 65., When it is desired to initiate the operation of the fluid motor, the knob 65 is depressed to move the spool 52 in an upward direction to the position shown in Fig. 2. In this position groove 55 in spool 52 will connect the inlet 35 with the top cylinder port 36 and fluid from the pressure source will then be applied to the upper end of the cylinder 44. This fluid will tend to move the piston 41 and ram 48 in a downward direction.

It will, be noted from Fig. 1 that the fluid motor 22 embodies a peculiar construction in that the piston 41 and ram 48 have a cylinder 66 formed therein. This cylinder receives a second piston 61 which is rigidly secured to and depends from the upper end of the casing 45. The piston 61 is provided with a central bore 68, the outer end of which communicates with a line 1|], this line being connected with the line 4| which is in turn connected with line 42 leading to reservoir 24. Line 10 contains a check valve indicated at 1|. It will be seen that when piston 41 moves in a downward direction, the second cylinder 66 will move relative to piston 61 to cause latter to be withdrawn from the former; when this motion occurs fluid will be drawn through lines 42 and 19 into the inner end of the cylinder 66. A branch line 12 extends from line.19 to the bottom cylinder line 46, the line 12 also containing a check valve 13. Purpose of line 12 and check valve 13 will be presently set forth.

From Fig. 2, it will be apparent that when valve spool 52 is fully elevated, groove 55 therein will establish communication between grooves 35 and 36 and between grooves 31 and 35, in the valve body 33. It will also be apparent that the spool 52 at this time prevents communication between groove 31 and exhaust groove 39, therefore, fluid supplied by the pressure source will be directed to the upper end of the power cylinder to cause piston 41 to be moved in a downward direction. This movement of piston 41 will discharge fluid from the lower end of cylinder 44 through line 46 to port 31 from which it will flow through groove 54 to groove 35 where it will combine with the fluid from the pressure source and be conducted through grooves 55 and 36 and line 43 to the upper end of the cylinder 44. It will thus be seen that the fluid from the under side of piston 41 will be transferred to the upper side thereofldecreasing the effective area of the upper surface of the piston 41 to the difference between the diameter of piston 61 andthe diameter of ram 48, the fluid introduced-from the pressure source being effective over this reduced area. Due to the reduction in effective piston area the ram and piston 41 will be caused to move at a rapid rate.

When the ram approaches the work the control knob 65 on lever 63 may be elevated to place the spool valve 52 in the position shown in Fig. 3, wherein communication between grooves 31 and 35 willbe interrupted and communication established between groove 31 and groove 39. The fluid then displaced by the piston 41 from the lower end of cylinder 44 will no longer be combined with the fluid applied to the upper end of cylinder 44 and the effective area of the upper surface of'piston 41 will be increased, this areaeasemen novwbei'ng*"equal' to: the: difference: hetweerntlie diameter; of. the: piston. 41 and that ofrpistonfil; this; area.- being exposed. to the. fluid fromithepressure. source. The rate: of. movement .of the piston 41'andram 48. will then decrease butthe force7exerted' by the ram will. be increased. The" distance. traveled by: the ram during: the power:

stroke may be regulated through the adjustments: ofzacollar T4 securedto the shipper rod. below; the; arm 6|. This collar: when engagedaby the. arm 6i will causetheshipper rod tot-move in ;a;; downward directionmoving with it .the spool-.521. When thisspool ismoved toi'the position shown. inrFig. 1, wherein the inletport. 35 iSICOIlIlGCtGd; through. grooves 55, 36 and 55. with: the exhaust-. groove 38, th fluid. pressurefrom. the pressure source will then be directedtorthe.reservoir'and: will not serve to move the piston; of. the: powerunit.. As previously: mentioned; the-.lineu-leading: from-:the: lower. end of the. power 'cylinderwill; then be -blocked, so that there will .be. no escape. of fluid contained therein. When the collar 14. is adjusted to secure this. operation suflicient force-will be supplied by the ram to theshippen rod to move the same even though the operator: attempts-to maintain the knob 650m the actuating l'ever.63 depressed., After the ram stops mov in'g it'may be caused to retract by releasing the. knob 65, or, elevating it,.to locate. the valve element 52 in the position shown in Fig; 4-.-v Under normal? conditions the collar l4"is disposed atuan point beyond the limit. of: the desired travel and: serves as a safety device to interruptthe down"- wardi'movement' of the ram. After the ram has: completed the desired travel in a. downward direction during normal operation the spoolmaybe'lowered to the position shown: in Fig. 4, releasing'knob 65; spring 58 will then expand? and move spool 52 to its lowermost position; When spool 52 occupiesposition.shown in Fig; 4,

groove 55 will establish communicationbetween. grooves 35 and 31; and fluid from the pressure: source will then be applied to' the lower end'roifi" cylinder 44. At this time, also, groove 5'6 will connect the top cylinder line 43' with. exhaust: port 38. The fluid thGIITSUPpIiGdZtO the:lower. end. of the power cylinder will cause the-piston 41 and".

ram 4 8130. move in anupward direction; the' fluidx.

exhausted from the upper endof the cylinder fiowingtofithe reservoir 24. This; upward movement ofpiston 41 and. cylinder. filicausespiston 6] to: displace fluid from the. inner. end of .cylinderxfifiy. this: fluid; flowingthrough passage 68, lines; 10; and I2 to line 46 where it will combine withifluid; from .the. pressure source. Through. the intro.-

duction" ofthe additionalfluid the efi'ectivearea: ofathe'under side of piston 41 will bereduced in an amount. equal to the area Of'iDlStOIl' l'i'l'makingv the. area of piston 41, whichis exposed to. the... fluidfrom the pressure source quite small. Be-

cause this effective area on the under surface: of the piston 41 is small the piston4'l and'ramJ48 Willbe caused to move upwardly. also ata rapid When the piston 41 approaches the upper limit? 6 positiomshownrin Rig; 231.011;.thatrshownsinl figr;3; r atzwhich timeacycle-of movement will .againzbee: initiated: When..the .spool..ocoupiesa the position shown inxFigs. 2 theramz. will ;.move.rapid1y as.

. described previously". After the" spool. occupies.

the: POSitlOIliShOWIl-ill Fig; 3 thexramwilllmove at a slowerirate', buttwith:increasediorce It. will be" observed that. in moving: from. the: positionvshowninllig; 1.. to that shown.in..Fig.. 2; thetspool 52 willpass through the position shown. in Figz13; It will. be: obvious from the drawing that the cylinder 66 and piston 61 function-.asiai, pumpwhenxpiston d'l reciprocates in cylinder. 44. On the suction stroke; which is accomplished:

during the-downward movement of piston 41, fluid;

will be'drawnintocylinder-fili, from the reservoir; check valve H permitting fluid flow inthis direction. Check valve 13 prevents the flow of fluid Hemline-46 and the bottom of cylinder. M during this movementofthe piston 41. On the re turn stroke of piston 41 check valvel'l preventsfluid'exhausted from cylinder 66 from fiOWingrtOlthe reservoir- 24'; while check valve 13 permits this exhaust fluid'to-flow into line 45.

Insome instances-it may bedesired to operate the pressram in the-conventional manner, thatis, without combining thedischarge from certainpor-tions' of the cylinder withfluid flowing toother portions of the same or other cylinders. To secure this varied form' of operation the hy draulic' system may be modified-as illustrated Fig. 5 wherein line-1 2 is-provided with a valve 15 which in the previously described operation of the system is maintained in an open position. A-

'connecting line 76 containing a normally closed valve-11 is dis-posed between the lines 43 a-nd 10: Whenitis desiredto operate the systemin a con-- ventional manner-,valvel5-is closed and valve T! is opened; At this time the control valve spool 52- should-'be-placed in the position shown/in Fig. 3 to efiect a pressing operation of the ram. When the spool 52* is so positioned fluid under pressure from the pressure source will flow from the" inlet port 35 through groove 55 togroove 36 from which=itwill flowthrough lines 43; i5 and lil into the upper end of cylinder 44 and the inner end of cylinder 66. This fluid will urge the ram in a downward direction, the effective area of the piston being thetotal area of' piston 41 and piston 61; Due-to the increased effective area the" movement of the ram will-beslow; but the force will be'increased. When the pressing stroke has been completed the valve spool 52 may then be moved to the position shown in Fig. 4, wherein line 43 will be connected with thereservoir while line 46 is connected with the pressure source: Fluid from the pressure-source will'thusbeintroduced to the'lowerend of-cyli'nder 44 which will cause piston 41 to move in an upward direction;

'Fluid' expelled by pistons- 41 and 6! will pass" of 'its travel the arm 5| will engagethescollartZJ and'move the shipper rod 57' and spool 52? inan-x upward. direction. until communication. between. grooves 35 and 31 is interrupted atlwhich time. piston 41 willcease to move. The" spool 52 will then occupy the position shown in Fig; v1: wherein"- thezfluid from. the pressure source is. directed to; the-reservoir to decrease theloadr on: the pump. The. ram will. remain. in; this; elevated; position. untilzthez-spoollfizz i'sa'agaim moved eithen'itoxztheir through lines 43 and 42 to reservoir 24. Therate of return of'piston 4'! will beat the conventional rate.

Also in some instances of operation it may be desired'to cause the ram to" move at the conventional rate during the initial portion of the-rte:-

turn stroke and then at an increased. rate duringi thezbalance of return stroke. Toprovide for such operation a secondshunt line 18 containing:

' a.n0rmall"y' closed check valve is provided;

7'5iventional rate and then closed during. the :-1 e.=*7

maining portion of such stroke. When valve80 is open, fluid discharged from cylinder 56 will flow directly to reservoir 24. After. the valve is closed, this exhaust fluid will be combined with fluid flowing to the lower portion of the cylinder 44 to increase the rate of return travel of the piston 41. During the operation of the system in this manner valve 11 will be closed while valve 15 will remain open. It is obvious that the operation of the system may be modified through the provision and operation of valves 15, 11 and 80.

While the form of embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow:

We claim:

1. In a hydraulic system, a source of fluid pressure; a power unit having piston means with at least three pressure responsive areas of different sizes; and fluid conducting and controlling mechanism between said power unit and pressure source, said mechanism being operative in one position to combine fluid displaced, by the first piston area with fluid from said source and apply the same to the second piston area to move said piston means in one direction and operative in another position to combine fluid displaced by the third piston area with fluid from said source and appl the same to the first piston area to move said piston means in the opposite direction.

2. In a hydraulic system, a source of fluid pressure; a power unit having piston means with pressure responsive surfaces of large, intermediate and small areas; fluid conducting and controlling mechanism between said power unit and said pressure source, said mechanism having a valve member operative in one position to simultaneously direct fluid from said source and fluid displaced by the piston surfac with the intermediate area to the piston surface with the large area and operative in another position to selectively direct the fluid from said source to the piston surface with the large area and the fluid displaced by the intermediate area to exhaust, said valve member also being operative in still another position to direct fluid from said source to the piston surface with the intermediate area and fluid displaced by the larger piston surface to exhaust, said fluid conducting means being operative to combine the fluid displaced by the small piston area with the fluid from said source applied to the intermediate piston area.

3. In a hydraulic system, a source of fluid pressure, a power unit having a cylinder and piston, the opposite surfaces of said piston having different effective areas; a control mechanism between said pressure source and said power unit, said mechanism having a movable valve operative in one position to simultaneously direct fluid from said pressure source and fluid discharged by the smaller piston surface to the larger piston surface to cause rapid movement of said piston in a predetermined direction, said valve being operative in another position also to direct fluid from said source to said smaller piston surface and from the larger piston surface to exhaust to cause movement of said piston in the opposite direction; and a pump device operated by said piston when moving in said opposite direction to add fluid to that supplied by said pressure source to said smaller piston surface to increase the rate of movement of said piston in said opposite direction.

4. In a hydraulic system, a source of fluid pres sure, a power unit having a plurality of cylinders of different diameter and a plurality of pistons disposed therein, said cylinders and pistons being relatively movable; control mechanism between said pressure source and said power unit; a movable valve in said mechanism, said valve being operative in one position to selectively connect both ends of one cylinder with said pressure source to cause rapid movement of the pistons in one direction and operative in another position to connect one end of said one cylinder with said pressure source and the other end to exhaust to cause movement of said pistons in such direction with increased force and operative in a third position to connect said other end to said pressure source and said one end to exhaust to cause reverse movement of said pistons; and a valved fluid conductor extending between the second of said cylinders and said pressure source, said conductor being operative when said other end of said one cylinder is connected with said pressure source to combine fluid exhausted from said second cylinder with fluid from said pressure source.

5. In a hydraulic system, a source of fluid pressure, a power unit having a plurality of cylinders of different diameters and a plurality of pistons disposed in said cylinders for movement relative thereto, said pistons being movable in unison; control mechanism between said pressure source and said power unit, said mechanism being operative in one position to selectively connect both ends of one cylinder with said pressure source and in other positions to connect either end thereto and the opposite end to exhaust; and fluid conducting means extending between another of said cylinders and said pressure source, said conducting means being operative when a predetermined end of said one cylinder is connected with said pressure source to combine fluid exhausted from another of said cylinders with fluid from said pressure source.

6. In a hydraulic system, a fluid pressure source having a reservoir; a power unit having a casing with a cylinder; a piston disposed for reciprocation in said cylinder, said piston having a second cylinder formed therein; a second piston stationarily supported by said power unit casing and disposed in said second cylinder; conduit with said pressure source and the opposite end,

with said reservoir.

'7. In a hydraulic system, a source of fluid pressure including a reservoir; a power unit having a casing provided with a cylinder; a piston disposed for reciprocation in said cylinder, said piston having a cylinder formed therein; a second piston disposed in the cylinder in the first piston, said second piston being supported by said casing; control mechanism for said power unit, said control mechanism having an inlet port communicating with said pressure source and cylinder ports communicating with opposite ends of the first-mentioned cylinder; conduit means connecting the inner ends of said cylinders; a.

check valve in said conduit means limiting fluid flow to a direction from the cylinder in said piston to the first-mentioned cylinder; a second conduit means connecting the second-mentioned cylinder with said reservoir; a check valve in said second conduit means limiting fluid flow to a direction from said reservoir to said second cylinder, and a movable valve spool in said control mechanism selectively operative to connect both ends of the first-mentioned cylinder with said power source simultaneously when in one position or either end with said power source and the other end with said reservoir when in other positions.

8. In a. hydraulic system, a, source of fluid pressure, a fluid motor having a cylinder and a piston disposed for reciprocation therein; control mechanism between said pressure source and said motor, said control mechanism having a casing with a chamber and inlet, top and bottom cylinder and exhaust ports communicating therewith; fluid conducting means connecting said inlet port with said pressure source and said cylinder ports with the ends of said cylinder; a valve element disposed in said chamber for move-ment to one position to establish simultaneous communication between said cylinder ports and said inlet and to other positions to establish communication between either of said cylinder ports and said inlet port and the other cylinder port and exhaust; a pump device operated by movement of said piston, said pump drawing fluid thereinto during movement of said piston in one direction and discharging fluid therefrom during movement of said piston in the opposite direction; and passage means for conducting the fluid discharged from said pump to the end of said cylinder connected with said bottom cylinder port.

9. In a hydraulic system, a source of fluid pressure, including a reservoir; a fluid motor comprising a casing having a cylinder formed therein; a piston with a ram disposed for reciprocation in said cylinder, said ram projecting through the end of said cylinder; a second cylinder formed in said piston and ram; a second piston carried by said casing and disposed in said second cylinder; a control mechanism having a body with a chamber and inlet, inner and outer cylinder and exhaust ports communicating with said chamber; fluid conductor means connecting said inlet port with said pressure source and the ends of said first cylinder with said inner and outer cylinder ports; a, valve element disposed in said chamber for movement to one position to connect both cylinder ports with said pressure source to cause a rapid projection of said ram from said casing,

said valve element also being movable to another position to connect the outer cylinder port with said'pressure source and the inner one with exhaust to cause the projection of said ram under increased force, said valve element being movable to a third position to connect the inner cylinder port with the pressure source and the outer cylinder port with exhaust to cause the retraction of said ram; passage means connecting the innerend of said second cylinder with the conductor leading from the inner cylinder port to the inner end of said first cylinder; additional passage means connecting the aforementioned passage with said reservoir; and check valve means in said passages to limit the direction of fluid flow therethrough.

10. In a hydraulic system, a source of fluid said inlet and an exhaust port and to block said bottom cylinder port, said element being operative in a, second position to establish communication between the bottom and top cylinder ports and said inlet port, the element being operative in a third position to connect said inlet and top cylinder ports and said bottom cylinder and exhaust ports, a fourth position of said spool element serving to connect said inlet and bottom cylinder ports and said top cylinder and exhaust ports; and check valve equipped conduit means for combining fluid displaced by one of the piston areas with fluid flowing from the pressure source when the spool element is in said fourth position.

11. In a hydraulic system, a source of fluid pressure having a reservoir; a power unit having a casing with a piston chamber; a piston and ram disposed for movement in said chamber, said piston and ram having a cylindrical chamber formed therein; a second piston carried by said casing and disposed in the chamber in said piston and. ram, movement of the first-named piston causing relative movement of the second piston in its chamber; mechanism for controlling fluid flow from the pressure source to said power unit and from the latter to exhaust, said mechanism having a casing with a bore and inlet, top and bottom cylinder and exhaust ports communicating therewith; fluid conducting means connecting said inlet port with said pressure source and said top and bottom cylinder ports with opposite ends of the first-mentioned chamber; a spool member disposed for movement in said bore, said spool serving in one position to connect said inlet and an exhaust port and in a second position to connect said inlet with both cylinder ports, said spool serving in a third position to connect said inlet with the top cylinder port and said bottom cylinder port with an exhaust port, a fourth position of said spool reversing the connections made in the third position; a conductor extending from the chamber in said piston to said reservoir; a check valve in said conductor to limit flow to the direction from said reservoir to said chamber; a conductor communicating with the lastnamed conductor and the conductor extending from the bottom cylinder port to said first-mentioned chamber; and a check valve in the lastmentioned conductor to limit flow in a direction toward the first-mentioned chamber.

CECIL E. ADAMS. WILLIAM D. PETERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,990,052 Sosa Feb. 5, 1935 2,320,759 Stacy June 1, 1943 2,379,180 Pohl June 26, 1945 

